1. Field of the Invention
The present invention relates to an illumination system and a projection device comprising the illumination system. More particularly, the present invention relates to an illumination system that performs wavelength transformation on a particular wave band light and a projection device using the illumination system.
2. Descriptions of the Related Art
Over recent years, with the continuous advancement of technologies for manufacturing projection devices, lightweight and slim projection devices have become the mainstream product in the market. The demands of new and improved products in the market have led to the continuous improvement of the design of projection devices. Accordingly, manufacturers of projection devices must develop various smaller projection devices with a high efficiency and better imaging quality to satisfy the needs in the market.
Referring to FIG. 1 a projection device 1 disclosed in U.S. Pat. No. 7,547,114. An illumination system 11 of the projection device 1 uses a single light source to project light to a color wheel 112. The color wheel 112 has green and red phosphor materials for reflecting or transforming a blue light emitted by a blue solid-state light source 111 (e.g., a light emitting diode (LED) or a laser) into a green light or a red light respectively. The green light and the red light are then provided to a projection device. However, such a projection device has too low of a luminous efficiency and wastes a large amount of light energy.
Referring to FIG. 2, there is shown another illumination system 21 of a conventional projector 2. Instead of using a single light source to project light to a color wheel, the illumination system 21 uses a blue solid-state light source 211, a red LED 212, and a wavelength transforming element 213 with a green phosphor material. Light rays that are reflected or transformed are focused into an imaging system for imaging. However, the blue light can be coupled with the green light and the red light that are formed through transformation only after being reflected multiple times, so the light energy of the blue light will be significantly attenuated due to the multiple reflections. Moreover, the light emitted by the LED is of a scattered nature, so a plurality of light condensing elements must be used to condense the light to improve luminous efficiency. Consequently, the projector 2 must be made to have a large internal volume to contain the light condensing elements, and this is in contradiction to the demands for lightweight and slim products in the market.
Accordingly, it is important to provide a projection device which features both a highly efficient illumination system and a small volume, as well as be able to reduce light energy waste and avoid color non-uniformity of a displayed image.